正
せい · sei · JLPT N3 · noun
true
正 = 一 line + 止 foot: a foot that stops right at the line is correct
The old form showed a foot (止) marching to a target line (一), which meant going straight to the right place. That gives the senses true, proper and regular. Sei sounds like say, so you can remember it as saying it straight.
正 — one 一 + stop 止
Originally an ideograph showing a foot (止) advancing toward a target line (一), meaning 'to march straight toward' a city or goal. From this came the senses 'upright,' 'correct,' and 'proper.' The military sense survives in 征 (to campaign), which took over the original 'march' meaning.